Method of and apparatus for multi-layer polymer plastic articles having interior core layers, with control of relative shifting of the position of the core layer and the relative thickness of inner and outer layers in the molded articles

ABSTRACT

A novel technique for molding multi-layer polymer plastic articles having inner, outer and interior or core layers by controlling relative volumetric flow rates of the inner and outer layers to enable relative shifting of the position of the core, and also the relative thickness of the inner and outer layers in the molded articles; and with leading, and, where desired, trailing ends of the interior layer flow into the mold cavity substantially positioned on the zero gradient of the velocity profile of the flowing polymer streams.

FIELD

[0001] The present invention relates to the co-extrusion of pluralitiesof flowing polymer plastic streams through nozzle extruders and the likeinto injection molding and similar apparatus for forming multi-layerplastic articles in which an interior core is encased by inner and outerlayers of the article; and, more particularly, to the control ofrelative volumetric flow rates of the layers for attaining greaterflexibility in the properties and relative thickness and positions ofthe layers in the ultimate article. More specifically, the invention isespecially, though not exclusively, useful with co-extrusion processesof the type described in my earlier U.S. Pat. No. 5,914,138, issued Jun.22, 1999 For Apparatus For Throttle-Valving Control For The Co-ExtrusionOf Plastic Materials As Interior Core Streams Encased By Outer And InnerStreams For Molding And The Like.

BACKGROUND OF INVENTION

[0002] A common problem in multilayer molding is the maintaining of auniform penetration of the leading edge of the interior core layer, whenthat layer is not near the zero gradient of the velocity profile of theflowing polymer stream as it flows through a hot runner nozzle and/orinto the mold cavity forming the molded article. Unlike the prior arttapered leading edge flow of, for example, systems of the type disclosedin U.S. Pat. Nos. 4,895,504 and 4,892, 699, my said earlier patentteaches the combining of the different flow streams of materials toachieve a velocity profile of the combined streams in the melt deliverysystem that is similar to the velocity profile of the combined stream inthe injection mold cavity, thereby insuring uniformity in a resultingmolded article.

[0003] This problem of maintaining uniform penetration of the leadingedge of the interior core layer when it is not close to the zerogradient of the velocity profile becomes particularly severe when thereis the requirement to form the multilayer article with the core layernot centered on the midplane of the article.

[0004] In two-material, three-layer preform molding, for example, it maybe desirable to have a barrier or scavenger layer closer to either theinner sidewall or outer sidewall of a blow-molded container article, inorder to enhance the barrier property of the container. Inthree-material, four-layer preform molding, this leading edge problemalso occurs, particularly when the volumetric flow rate of one of theinterior core layers is greater than that of the other interior corelayer.

[0005] Another common current problem also arises in using post-consumerrecycled plastic (PCR) in a molded article that consists of layers oftwo other polymers. Current art accomplishes this three-materialcombination by using apparatus and methods that create a 5-layerarticle. With such 5-layer technology, however, the molding cycle timesare significantly longer than if the article had been molded of only onematerial. Such 5-layer molded articles, moreover, suffer delamination ofthe layers if the second polymer has low adhesion to the virgin skinlayers and to the central PCR layer.

[0006] The present invention is directed to the solution of the aboveproblems, and limitations, among others, in such prior art systemsthrough a later-described technique for permitting changed or controlledvariation of the relative volumetric flow rates of the inner and outerlayers after the flow of the interior core layer stream has started.

OBJECTS OF INVENTION

[0007] A principal object of the present invention, accordingly, is toprovide a new and improved method of and apparatus for moldingmulti-layer polymer plastic articles having inner, outer and interior orcore layers that shall not be subject to such problems and limitations;but that, to the contrary, obviate such through the control of relativevolumetric flow rates of the inner and outer layers in such a way as toshift the position of the core and control also the relative thicknessof the inner and outer layers of the article.

[0008] Another object is to provide novel apparatus and methods toinject the leading edge of the interior core layer on the zero gradientof the combined velocity profile during the initial portion of theinterior core layer flow, and then to change the relative volumetricflow rates of the inner and outer layers to cause the later orsubsequent portion of the interior core flow to be offset from the zerogradient of the combined flow velocity profile.

[0009] An additional object is to provide novel apparatus and methods torestrict either the flow of the inner or of the outer layer volumetricflow rate in order to shift the interior core layer trailing portioninside or outside the 50% streamline through the nozzle and into themolded part.

[0010] Still a further object of the present invention is to provide anovel method and apparatus to produce an article of three materialsmolded into four layers.

[0011] Another object is to provide in such apparatus, novel operationwherein the leading edge of one of the interior core layers is injectedon the zero gradient of the velocity profile of the combined streambefore the start of flow of the other interior core layer.

[0012] Other and further objects will be described hereinafter and aremore fully delineated in the appended claims.

SUMMARY

[0013] In summary, however, from one of its important aspects, theinvention embraces a method for co-extruding multiple plastic materialsas for injecting through a gate region into a mold cavity to produce amolded article, that comprises, co-extrusively flowing streams ofplastic materials with at least one interior stream that is to serve asan interior core of a resulting molded plastic article within inner andouter streams of plastic material that serve as covering wall plasticmaterial layers for the core; forcing the flowing streams to flow alongconcentric annular flow paths within and along a longitudinallyextending tubular extruder nozzle to the cavity gate region; adjustingthe flow streams initially to cause the core stream to start to flow ata region of substantially zero gradient in the transverse flow velocityprofile of the extrusion; thereupon varying the relative volumetric flowratio of the inner and outer layer streams after the zero-gradient flowof the core layer has started in order to offset the core layer flowfrom the zero-gradient and to shift the core layer closer to one of theinner or outer annular flow boundaries, thereby to produce a moldedarticle wherein the major portion of the core layer is closer to one ofthe inner or outer article walls than the other.

[0014] Preferred and best mode designs and configurations are laterdescribed in detail.

DRAWINGS

[0015] The invention will now be described in connection with theaccompanying drawings, FIG. 1A of which is a schematic longitudinalsection of the type of nozzle described in my above-mentioned patentusing a central longitudinal restrictor or throttle pin to forceconcentric annular flow of the injected plastic thereabout within thewalls of the hollow extruder nozzle; and FIG. 1B is a graph illustratingresulting flow fraction and velocity profile curves across the annularchannel within the nozzle of FIG. 1A for an inner flow-to-outer flowratio of 50:50—the ordinate plotting the ratio of flowvelocity-to-average velocity as a function of the radius of the annulusbetween the inner and outer nozzle wall, with the central solid linecurve VP plotting said ratio and showing zero gradient for the corestream CF (shaded vertical strip), and the curve designated with acircle marker, plotting the flow IF between the radius and the throttlepin T from the inner to the outer wall, and the curve marked with atriangle, plotting the flow OF between the outer wall and the annularradius;

[0016]FIG. 1C is a graph showing the relative timing and proportions ofvolumetric flow rate of the combined inner and outer layer flows, theinner layer flow, and the interior core layer flow, with FIGS. 1D and 1Ebeing similar to FIG. 1A, but showing partially and completely filledconditions of the mold cavity fed from the throttled nozzle for theconditions of FIG. 1B;

[0017]FIGS. 2, 2A, 2B and 2C correspond, respectively, to the showingsof FIGS. 1B, 1C, 1D and 1E, but for an inner-to-outer flow ratio of40:60;

[0018]FIGS. 3, 3A, 3B and 3C respectively correspond to FIGS. 2, 2A, 2Band 2C, but for an inner-to-outer flow ration of 60:40;

[0019]FIGS. 4 and 5 are velocity profile graphs similar to FIG. 2, forrespective ratios of 25:75 and 75:25, with FIGS. 4A, B and C and FIGS.5A, B and C corresponding to FIGS. 2A, 2B and 2C, respectively, but forsuch 25:75 and 75:25 ratios, respectively;

[0020]FIG. 6 is a flow fraction and velocity profile similar to FIGS.1A, 2, 3, 4 and 5, but embodying the methodology of the presentinvention, with an initial portion of the core layer flow occurring fora 50:50 ratio, and the major flow occurring with 80:20 ratio to shiftthe core toward the outer wall, but without providing any leading-edgebias;

[0021]FIGS. 6A, 6B and 6C are similar to respective FIGS. 5A, 5B and 5Cbut describe the operational conditions of the invention as reflected byFIG. 6;

[0022]FIGS. 7, 7A, 7B and 7C correspond to respective FIGS. 6, 6A, 6Band 6C, illustrating the operation of the invention for the conditionsconverse to FIG. 6, wherein, after the initial 50:50 flow ratio, theinner flow-to-outer flow ratio is decreased without shifting the initialcore layer leading edge, the core layer being shifted towards the innerlayer;

[0023]FIGS. 8 and 9 are graphs similar to FIGS. 3A-6A for modificationswherein the core is shifted back before the end of the flow, as shown inFIGS. 8A, B, C and D for original core shifts towards and away from theinner wall; and, in FIGS. 9A, B, C and D, for original core shifts awayfrom and towards the inner wall, respectively;

[0024]FIGS. 8E through 8I are respectively similar to FIGS. 8 and 8A-8D,but are designed for producing flat-shaped molded articles;

[0025]FIGS. 9E through 9I similarly correspond to FIGS. 9 and 9A-9D, butrelate to molding flat-shaped articles;

[0026] FIGS. 10A-C are schematic top views of the inner, outer and coreflow entry channels and flow restrictor controls for varying theinner/outer channel flow ratios for the core shifting effects of theinvention;

[0027]FIGS. 11A and B are similar views with flow restrictor controlsdisposed in the most common channel feeding the respective outer andinner layers,

[0028]FIGS. 12A, B and C are schematic views of pin-type flowrestriction elements;

[0029]FIG. 13 is a cross-section of a preferred nozzle-flow controlapparatus for the practice of the invention;

[0030]FIGS. 14 and 15 are enlarged cross-sections of varying flowcontrol positions of operation of the nozzle of FIG. 13;

[0031]FIGS. 16A and B are similar to FIGS. 10A-C, but are directed tofeed channels for three-material streams to each nozzle to form innerand outer annular covering layers.

[0032]FIGS. 17 and 17A-D are 19 and 19A-D illustrated the adaptation ofthe techniques of the invention for producing three-material, fourlayered articles, and illustrating graphs in FIGS. 17 and 19 showingrelative timing and proportions of volumetric flow rate of combinedinner and outer layer flow, the innermost interior layer flow and theoutermost interior layer flow of two different three-material, fourlayer flow systems;

[0033] FIGS. 18, 18A-D, FIGS. 20, and 20A-D are views similarrespectively to FIGS. 17 and 17A-D and FIGS. 19 and 19A-D, but aredirected to the molding of flat-shaped articles rather thancylindrical-shaped containers and the like.

[0034]FIGS. 21A, 22D, 23D and 24D show various exemplary types ofcontainers that may be formed by the techniques of the invention fromrespective per-forms 21B-C-D, 22, 23 and 24; respective enlargedcross-sectional segments A, B and C of which are illustrated in FIGS.22A-C, 23A-C and 24A-C.

PREFERRED EMBODIMENTS OF THE INVENTION

[0035] In my before-referenced prior co-extrusion patent, at leasttwo-polymer plastic materials are provided as a 3-layer combined flowstream; a first material L which forms the ultimate outer and innermolded covering layers of the ultimate molded product, article or partfrom the inner and outer flow stream layers (IL and OL), injected asannular streams; and a second material (I) which forms the middle, inneror interior core of the product formed from an injected concentricannular interior stream (IA) encased within the inner and outer annularstream layers of the covering material.

[0036] The preferred apparatus employs a multiple-plastic streamco-extruder as for injection molding cavities in which the extruder isinternally provided therewithin and therealong with a restrictor orthrottle pin, rod or element that forces combined plastic materialsstreams, formed with an interior core stream encased in outer and innerstream layers, into corresponding concentric co-extensive annular flowstream layers that are ultimately split transversely in oppositedirections into a cavity gated to the extruder, and with the core streamat a region of zero gradient in the transverse flow velocity profilewithin the extruder and cavity.

[0037] Referring to FIG. 1A, a schematic cross-sectional view of alongitudinally extending extruder nozzle N is shown provided with acentral longitudinal throttle needle or pin acting as a flow restrictorT downstream of a combining section C, providing uninterrupted continualannular flow within the extruder of the concentric inner and outerannular stream layers IL and OL, with the encased interior annular corestream IA, and into gate G. The combined streams A are then, as beforestated, laterally split and injected transversely in opposite directionsinto a molding cavity (CAV)—shown for illustrative purposes of shapesuitable for molding cylindrical containers such as bottles or the like.As described in my said prior patent, other shaped cavity molds may alsobe used for other products, as may a wide variety of plastic materialsbe used, among them, for example, polyethylene, PET, and other plasticand polymer compositions, as later more fully described.

[0038] As further taught in my prior patent, it is highly desirable inmany applications that, as shown in FIG. 1B, the core layer flowssubstantially on the zero-gradient velocity profile (O) in order to keepthe leading edge of the core layer uniform 360-degrees around aperiphery of the annular flow, to insure, as the flow enters the cavity,that the core layer is uniformly distributed in the cavity, with thehighest point of the velocity typically on the center line of the flow;and wherein 50 percent of the material is on the inside of thestreamline and 50 percent is outside the streamline, and the zerogradient occurs right on the 50-percent streamline.

[0039] In FIG. 1C, a graph is presented plotting as a function of time,the volumetric flow rate of the combined inner and outer flow (topcurve), the inner layer (IL) flow (dash-line curve) and the interiorcore layer flow (bottom curve) encompassing the times A and B,respectively representing a time after the start of the interior corelayer flow, and an intermediate time before the leading-edge of the corelayer has left the extruder to enter the mold cavity. FIG. 1D is alongitudinal section similar to FIG. 1A for the partially filledcondition at time B, and FIG. 1E shows the completely filled cavity,demonstrating the distribution of the core layer extending most of theline length of the flow in the cavity and having a uniform leading edgeat a 180-degree section of the cavity and with the core layer placed onthe 50% streamline in the middle of the molded article.

[0040] My earlier patent also provided for moving the throttle orrestriction pin to vary the percentage of the outer layer material inthe inner annular flow layer vs. the outer annular flow layer of thecombined flow stream downstream of the combining area. Changing therelative volumes of the outer layers shifts the position of the core(interior) layer in the mold cavity to produce a part with controlledouter layer thickness on both surfaces of the molded article or part. Ifthe outer layer flow is biased toward either the inner or outer annularflow layers, the outer layer thickness in the molded part will besimilarly biased on the corresponding surface molded from the biasedannular layers. Material from the inner annular flow layer forms thesurface layer of the part molded by the cavity wall opposite the gateinto the cavity and the material from the outer annular flow layer formsthe surface layer of the part molded by the cavity wall adjacent to thegate.

[0041] The use of a movable throttle valve pin is typically appropriatein cases where it is the advantageous to vary, during each injection,the relative percentage of the outer layers material in the innerannular flow layer vs. the outer annular flow layer. For cases where therelative thickness of the layer on both surfaces of the molded part canremain in fixed proportion to each other, the embodiment uses anon-moving throttle valve pin.

[0042] A typical injection time-line for such three-layers moldedarticles is as follows: Time, Seconds Action 0   Close mold 0.1 Startinjection of inner and outer layer material at substantially 50:50 ratio0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Start injection of interior layermaterial on zero-gradient of velocity profile 1.1 1.2 1.3 1.4 1.5 1.61.7 1.8 1.9 2.0 Finish interior layer injection on zero-gradient ofvelocity profile >2.0   Finish injection of inner and outer layermaterial

[0043] It has now been discovered that if, instead of changing therelative percentages of inner and outer annular layer volumes ofmaterials to obtain unequal covering thicknesses, as described in myearlier patent, one starts the flow process with the innerlayer-to-outer layer volume flow being equal (ratio of 1), this willstart the initial portion of the interior or core layer flow, along thedesired zero-gradient velocity profile; and then, during the continuedflow, the ratio of inner-to-outer layer flow may be changed to effectcore layer shifting as later more fully described.

[0044] In accordance with the present invention, the core layer flow isthus started on the zero-gradient velocity profile, with the inner layerin the combined flow and the outer layer in the combined flow bothhaving the same volumetric flow rate at the time the core material layeris introduced. Shortly after so introducing the core layer to create theleading-edge of the core layer, the invention enables the changing ofthe ratio of inner layer-to-outer layer flow, advantageously to placethe remaining portion—preferably about 90 to 95 percent of the corelayer that is flowing into the cavity—to be shifted towards the outsideboundary wall or towards the inside boundary wall of the molded article.In this way, the advantages of knowledge of the zero-gradient velocityprofile is combined with the advantageous shifting of the position ofthe core layer to enhance the function of the molded article—theshifting of the volumetric flow of the inner layer vs. the outer layer,causing the shift of position of the core layer.

[0045] As earlier described, FIG. 1B shows operation with the type ofnozzle described in my above-referenced patent, employing a throttle pinadjustment such as to produce substantially a 50:50 inner flow(IF)-to-outer flow (OF) ratio, placing the leading-edge of the interiorlayer flow IL on the zero gradient of the combined velocity profile, andenabling the absence of any leading edge bias in the molded article dueto flow velocity.

[0046]FIG. 2 is an operation showing similar to FIG. 1B wherein thethrottle pin adjustment has been positioned to achieve an innerflow-to-outer flow ratio of 40:60, rather than the 50:50 ratio of FIG.1B, placing the leading-edge of the interior layer IL near the zerogradient of the combined velocity profile. This produces a small, butacceptable leading edge bias in the molded article, as also explained inmy earlier patent.

[0047]FIG. 2A presents the same type of volumetric flow rate graph forthe operation of FIG. 2 as described in connection with FIG. 1C for theoperation of FIG. 1B; and FIGS. 2B and 2C illustrate partially fillednozzle-cavity flow conditions at time B and for complete cavity filling,respectively.

[0048]FIG. 3 illustrates similar operation but showing the ratio ofinner flow-to-outer flow as 60:40, as opposed to FIG. 2. Again, asdisclosed in my previous patent, the core layer (CF) remains close tothe zero gradient, producing only a small but acceptable leading edgebias, this time towards the outer wall. Thus, though shifting the corelayer either toward the inner wall or toward the outer wallapproximately 10 percent of the wall thickness, a reasonable andacceptable leading edge bias is still maintained. FIGS. 3A, B and C,correspond respectively to FIGS. 2A, B and C, above explained, but aredirected to the operation of FIG. 3.

[0049] In FIG. 4, however, a condition is shown for a flow ratioadjustment of 25:75, inner flow-to-outer flow, wherein the core-layerflow CF is now well offset away from the zero gradient of the combinedvelocity profile, resulting in a velocity distribution bias of the corelayer that produces a large leading edge bias that creates anunacceptable molded article. In FIGS. 4A, B and C, corresponding to thetype of showings in respective FIGS. 2A, B and C, the operation for theconditions of FIG. 4 are similarly presented.

[0050]FIG. 5 shows the case where the inner-to-outer flow is 75:25,again illustrating the bias created in the molded article; and FIGS. 5A,B and C correspond to FIGS. 2A, B and C, respectively, but illustratethe conditions of FIG. 5, with a flow Δv (FIG. 5B) producing a largebias Δl (FIG. 5C).

[0051] As before stated, however, in accordance with the discoveryunderlying the present invention, the core layer may indeed be shiftedfor useful purposes without having the resulting molded article sufferan unacceptable leading edge bias caused by the velocity bias. Thecritical operational requirement for achieving this novel result isgraphically illustrated in FIG. 6, and involves, as earlier discussed,that necessity for employing an initial throttle pin adjustment or otherflow restrictor adjustment that ensures that the initial portion of thecore or interior layer flow occurs when the inner flow (IF)-to-outerflow (OF) is in a substantially 50:50 ratio to place the interior corelayer leading edge on the zero gradient of the combined velocityprofile, as at region I in FIG. 6. After that flow is well-establishedat I—(of the order of a flow of a few, preferably about 5, percent (+)of the core material that is to be flowed for the molding of thearticle), then it has been found that a subsequent throttle pinadjustment or other flow-restrictor adjustment at region II, as in thecase of FIG. 6, increases the inner flow-to-outer flow ratio, resultingin shifting the interior core layer leading edge. The resulting moldedarticle—in this case, having about an 80:20 ratio with the majority ofthe core layer flow length III in the molded article extending closer tothe outer wall—will not produce a leading-edge bias caused by velocitybias, and will still enable the production of the uniform leading edgeon the molded article, but with the majority (say 95%) of the core layerlength shifted toward the outer wall, as for purposes earlier and alsohereinafter discussed.

[0052] One of such purposes for positionable core layers is as barrierlayers, where a humidity sensitive barrier layer may be required withinthe molded article such as a cylindrical bottle container or the like.There may be advantage to shifting the barrier layer towards the outsidewalls of the container, away from the liquid content and thus at a lowerrelative humidity environment that can enhance the performance of thebarrier layer and even require less volume of barrier material in orderto provide the same barrier effect to the contents. Another illustrationis for use of oxygen scavenging layers, the scavenging capacities ofwhich may be increased by being in a higher relative humidity and/orbeing closer to the contents as opposed to being close to the outsidewall. A thicker container outer layer, moreover, would permit lessoxygen permeation than if the outer layer were thinner, slowing downoxygen transfer from the outside to the scavenging layer. The scavengingcapacity of a scavenging layer closer to the contents would also removeresidual oxygen left in the contents of the container during the fillingprocess.

[0053] While the invention is useful with all kinds of polymers,polyethylene terephthalate (PET) is highly desirable for container skinmaterials; nylons and ethylene vinyl alcohols are useful for barrierproperties; scavenger materials include products such as BP-Amoco“Amasorb”, and compounds of heavy metals like cobalt with MXD6 nylon, orethylene vinyl alcohol, wherein the cobalt makes the nylon or alcoholreactive to oxygen, as in chemical scavenging reaction therewith, ratherthan allowing oxygen permeation through the materials; and combinations,such as the above, will provide both barrier and scavenger properties.The incorporation of metal powders in the polymer can provideelectromagnetic energy barrier layers, as well. Through the technique ofthe invention, indeed, any desired position of the core layer and of therelative thicknesses of the inner and outer layers of the article canreadily now be obtained through this novel control of relativevolumetric flow rates of the inner and outer layers above explained.

[0054] This is illustrated in the graph of FIG. 6A, where the innerlayer flow increase (step S¹ in the dash-line curve) occurs after thestart S of the core flow with 50:50 inner layer-outer layer flow to theleft of S¹; at time A. As shown in the filled cavity of FIG. 6, thoughnearly all the core length is shifted towards the outer wall, noleading-edge bias exists in the article, and where the leading edgeremains on the zero gradient.

[0055] The converse of the operation of FIGS. 6A, B and C, is shown inFIGS. 7A, B and C, where, after the initial portion I of the interiorcore layer flow occurs during an inner flow-to-outer flow ratioadjustment of substantially 50:50,placing the core layer leading edge onthe zero gradient of the combined velocity profile, the throttle pin orother flow restrictor is then adjusted to decrease the innerflow-to-outer flow ratio, again without shifting the interior layerleading edge—this time resulting in a molded article with the bulk ofthe core layer shifted toward the inner wall in the same ratio of 80:20,and again with no leading edge bias caused by velocity bias (FIG. 7C).

[0056] A typical injection time-line for systems of the invention suchas those of FIGS. 6 and 6A-C and 7 and 7A-C is as follows: Time, SecondsAction 0 Close mold 0.1 Start injection of inner and outer layermaterial at substantially 50:50 ratio 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.91.0 Start injection of interior layer material substantially on zero-gradient of velocity profile 1.1 Change ratio of inner layer:outer layerflow rates 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Finish interior layerinjection (trailing edge offset from zero- gradient of velocityprofile) >20 Finish injection of inner and outer layer material

[0057] The invention, moreover, provides not only for shifting the corelayer to one side or the other of the article, such as a hollowcontainer, and for relatively varying the thickness of the inner andouter layers, but also for enabling the shifting of the core layer backinto another position of the article. Examples of this are shown inFIGS. 8A 8B, 8C and 8D for the operation graphically represented in FIG.8 and in FIGS. 9A-9D for the operation graphically represented in FIG.9.

[0058] Turning first to FIGS. 8 and 8A-D, in accordance with thisembodiment of the invention, the flow starts at zero-gradient velocityprofile (I in FIG. 8A—top curve in FIG. 8); shifting the core layertoward the inside wall (II-III in FIG. 8B) by decreasing the inner layerflow (at S₁ in FIG. 8, between times A and B); and, near the end of theflow (between times C and D), increasing the inner layer flow back toequality with the outer layer flow (S₂ in FIG. 8) to shift the corelayer (at II′ in FIG. 8C) back to the zero-gradient profile (at III′ inFIG. 8C), thereby producing the shape shown in FIG. 8D.

[0059] A useful purpose for the operation of FIG. 8 resides instructural considerations, wherein there may be a highly stressedportion of the molded article that can cause mechanical failure, such asdelamination of the article, with the barrier or core layer positionedcloser to the inside wall. Secondly, it can be important to control thethickness and shape of the terminal end of the core flow—the lastportion of the molded article to freeze or solidify. Injection moldingof the hot plastic into the cold cavity causes the molded article tofreeze or solidify from the inner surfaces toward the interior layer,and it is advantageous to control the final flow of the materialentering the cavity along the 50-percent streamline.

[0060]FIGS. 8 and 8B-D thus illustrate the shifting of the majority ofthe core flow towards the inside boundary wall, with both theleading-edge and also the trailing or terminal end on the zero gradient.

[0061] While the invention has heretofore been illustrated in connectionwith molding bottle or cylindrical-shaped container applications, thetechniques of the invention are useful for molding other shaped articlesor objects as well, including, as a further illustration, flat-shapedmolded articles. FIGS. 8E-I illustrate such a flat-shaped molded articleapplication, with the views corresponding respectively to theabove-described FIGS. 8 and 8A-8D for a hollow bottle or the like.

[0062] Similarly, in the embodiment of the invention shown in FIGS. 9and 9A-9D, the flow starts at zero-gradient velocity profile (I in FIG.9A—top curve in the graph of FIG. 9); shifting the core layer toward theoutside wall (II-III in FIG. 9B) by increasing the inner layer flow (atS₁ ¹ in FIG. 9, between times A and B); and, near the end of the flow(between times C and D), decreasing the inner layer flow back toequality with the outer layer flow (S₂ ¹ in FIG. 9) to shift the corelayer (at II′ in FIG. 9C) back to the zero-gradient profile (at III′ inFIG. 9C), thereby producing the shape shown in FIG. 9D.

[0063] FIGS. 9-9B-D thus illustrate the shifting of the majority of thecore flow towards the outside wall, with both the leading-edge and alsothe trailing or terminal end on the zero gradient.

[0064] A useful injection time-line for the systems of FIGS. 8, 8A-D, 9and 9A-D follows: Time, seconds Action 0 Close mold 0.1 Start injectionof inner and outer layer material at substantially 50:50 ratio 0.2 0.30.4 0.5 0.6 0.7 0.8 0.9 1.0 Start injection of interior layer materialsubstantially on zero- gradient of velocity profile 1.1 Change ratio ofinner layer:outer layer flow rates 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9Return ratio of inner:outer layer flow rates to substantially 50:50 2.0Finish interior layer injection substantially on zero-gradient ofvelocity profile >20 Finish injection of inner and outer layer material

[0065] FIGS. 10A-C are schematic views looking from the top of thenozzle N, illustrating the entry flow channels or ports feeding theinner, outer and core or interior layer flows (IE, OE, and CE,respectively) from their respective sources (FIGS. 10B and C), andsurrounding a central throttle pin entry point TE. This flow channelarrangement is shown embodied in FIGS. 10B and 10C with an array of fournozzles, fed initially from an outer and inner layer source O/IS and acore or interior layer source CS, respectively, in a balancedthree-layer flow system. The outer and inner layer plastic flow from thesource O/IS is split at S¹ into two matched flow streams, and thenbranched at B¹ to feed the entry channels for the outer layer OE andinner layer IE of each of the upper and lower pairs of nozzles, inparallel. Similarly, the core layer source CS branches to feed the corechannels CE of the two pairs of nozzles and with balanced feed.

[0066] Flow restrictor controls, such as well-known electrically,hydraulically or even manually operated valves, are substantiallyillustrated in FIG. 10B at FR, placed in each of the outer layer feedchannels and synchronously operated to vary the relative ratio of outerand inner layer flow at preselected times, for the previously describedflow shifting purposes of the invention. Similarly, in FIG. 10C, thesame controls can be effected with the flow restrictor controls FRdisposed in the inner layer feed channels within each nozzle or in eachfinal channel feeding material to the inner layer in each nozzle. Thus,in the embodiments of FIGS. 11A and B, the flow restriction control isshown inserted in the most common feed channel feeding the outer layerand the inner layer, respectively, for changing such flow ratios.

[0067] Schematic views, showing a simple but effective way of operatingpin-type flow restrictors in a feed channel are shown in FIGS. 12A, Band C for three different positions. FIG. 12A illustrates the leastrestricted position with the restrictor pin barely inserted into theflow channel; and FIGS. 12B and 12C illustrate more and mostflow-restricting positions, respectively. These may be effected, asbefore indicated, in the most common channel of the runner system (FIGS.11A and B), or, if desired, in a least common channel to the nozzle(FIGS. 10B and C) and elsewhere, as desired. Again, as earlier stated,the restrictor insertion and withdrawal control may be automaticallyeffected in well-known manner, electrically or hydraulically, forexample, with timing control of the position of each with respect tostart or the end of the flow—all as intended to be schematicallyrepresented at FR.

[0068] Turning, now, to specific practical designs for such nozzlechannel flow and restriction structures, reference is made to FIG. 13which illustrates a cross-section of a preferred hollow nozzle extruderconstruction of the form described in my said earlier U.S. Pat. No.5,914,138 (FIG. 16 thereof), in which flow from a manifold is effectedthrough a flat disc 3-layer flow combining area C-FD surrounding acentral longitudinally movable throttle valve pin T-T¹, and whereinannular flow is combined and gated into a mold cavity CAV. The flat discstructure FD comprises four flat discus surrounding the throttle pin Tand forming the inner flow channel wall C′ for the inner layer of thecombined flow stream. Flow channels C₁′, C₂′, C₃′ etc. are createdbetween the three mating planar surfaces of the discs FD, as alsoexplained in said patent, uniformly to disperse each flow layer toproduce a uniform flow of the respective material flowing from eachchannel into the area of combination C. In this manner, each layer ofthe combined flow stream is uniformly annularly disposed as it flowsfrom the combining means through the extruding throttle nozzle and gateG into the cavity CAV. The movable throttle valve pin T-T¹, undercontrol of an upper adjusting restrictor-control rod R, which is also,in a sense, part of the throttle pin structure as well, varies thepercentage of the outer layer material in the inner annular flow layerversus the outer annular flow layer of the combined flow streamdownstream of the combining area C. As before explained, changing therelative volume of the outer layers shifts the position of the core(interior) layer for the previously described purposes of the presentinvention.

[0069] In the embodiment above FIG. 13, the restrictor rod R axiallymovable within the nozzle inner housing E, is shown at R¹, just at theinner layer feed channel C₁′. This is a neutral position with discchannels C₁′, C₂′, etc. opened to balance inner layer flow with respectto the outer layer flow for the purposes of the initial core layer flowin accordance with the principles of the invention. In the enlargedviews of FIGS. 14 and 15, the throttle valve T has been adjusted by therod R to an elevated position R″, to increase the inner flow rate withrespect to the outer layer flow rate for the core shifting controlpurposes of the invention—the least flow-restricted position; whereas,in FIG. 15, more restriction (most) is illustrated at R′″.

[0070] A schematic feed channel diagram similar to FIGS. 10A-C, but forthe specific annular layer flow of the nozzle of FIGS. 13, 14 and 15when used for 3-material polymer plastic streams, is illustrated inFIGS. 16A and 16B. The inner and outer stream is divided within thenozzle to form the inner and outer annular covering layers. In thiscase, the source O/IS of the inner and outer layer flows, is againbranched into the nozzle entry feed channels, but a first interior layersource CS branch feeds the entry channel CE₁, and, as shown by the dashlines, a second interior layer source CS₂ branch-feeds the entry channelCE₂. The first interior layer stream (#1) is thus directed within thenozzles N to form the interior annular layer adjacent the inner layer.The second interior layer stream (#2) is directed within the nozzle toform the interior annular layer adjacent the outer layer.

[0071] As earlier mentioned, the techniques of the present invention arenot restricted in the numbers of materials and layers to be molded,though illustrating two-material, three-layer pre-form molding examples;it having been previously noted that the invention is also quite useful,for example, in three-material, four-layer pre-form molding as well.Such an application is shown in FIGS. 17 and 17A-D and FIGS. 19 and19A-D for molding hollow container articles or objects, and in FIGS. 18and 18A-D and FIGS. 20 and 20A-D for flat-shaped articles, respectively.

[0072] In connection with the adaptation of the invention for molding ofthree materials to form a four-layer object, typical applications wouldbe for a plastic container composed of two interior layers; one layerwould usually be selected for its gas barrier for gas scavengerproperties, and the other interior layer would be selected for someother property such as a structural layer or a recycled layer. The gasbarrier and/or gas scavenger property still requires that the leadingedge of this one of the two interior layers be uniform in itspenetration around the circumference of the molded object. This uniformpenetration can be achieved by starting the flow of this one interiorlayer before starting the flow of the second interior layer, so that theleading edge of this first-flowing interior layer starts on the zerogradient of the velocity profile. Subsequent initiation of the flow ofthe second interior layer offsets the later-flowing portions of thefirst interior material from the zero gradient, but the uniform leadingedge is established by the initial flow of the first interior layer onthe zero gradient.

[0073] In FIG. 17, the first-flowing interior layer C1 (in this case theoutermost interior layer in the molded object) starts to flow at timeS1. The second-flowing interior layer C2 (in this case the innermostinterior layer) starts flowing at time S2 which also corresponds withthe reduction of the flow rate of the combined inner and outer layerflow. FIG. 17A shows the flow in the nozzle and partially-filled cavityat time A of FIG. 17; this time being between the time S1 and S2. Thefirst-flowing interior layer C1 leading edge is on the zero gradient ofthe combined flow velocity profile, thus assuring its uniformpenetration in the molded object. FIG. 17B shows the partially filledcavity at time B of FIG. 17. The leading edge of the first-flowinginterior layer C1 remains on the zero gradient, while the later-flowingportions of the first-flowing interior layer are moved off the zerogradient by the second-flowing interior layer C2, and are closer to thewall of the extruder. FIG. 17C shows the position of the flows in thenozzle and cavity at time C of FIG. 17. The second-flowing interiorlayer has ceased flowing at time S3, thereby allowing the final flowportion of the first-flowing interior layer to return to the zerogradient just before its flow is terminated, S4. FIG. 17D shows thefilled cavity when the trailing edge of the first-flowing interior layerhas been injected into the cavity by the continued flow of the combinedinner and outer layer flow after time C, of FIG. 17. The filled cavityshows the first-flowing interior layer closer to the outer wall in theportions of the filled cavity corresponding to the simultaneous flow ofthe second-flowing interior layer.

[0074]FIGS. 19, 19A, 19B, 19C, and 19D are similar to FIGS. 17 and 17A-Din concept, except that, in this example, the first-flowing interiorlayer C1 is the innermost interior layer and the second-flowing interiorlayer C2 is the outermost interior layer. All other features are similarto the case of FIGS. 17 and 17A-D, but in the filled cavity, thefirst-flowing interior layer is closer to the inside wall of the moldedpart in portions of the cavity corresponding to the simultaneous flow ofthe second-flowing interior layer.

[0075] In both the embodiments of FIGS. 17, 17A-D and 19 and 19A-D, C2is shown terminating before the termination of C1 in order to allow thefinal portion of C1 to flow along the zero gradient of the velocityprofile. It should be understood, however, that it is within the scopeof this invention that C1 may also terminate before or simultaneouslywith the termination of C2 if the desired properties of the moldedobject are enhanced by such a termination sequence.

[0076] The operational graphs of FIGS. 17 and 19 show a reduction in theflow rate of the combined inner and outer layer flow at time S2,corresponding to the start of the flow of the second-flowing interiorlayer. The thickness of each of the flowing layers is directlyproportional to the volumetric flow rate of each layer relative to thetotal volumetric flow rate of each layer relative to the totalvolumetric flow rate of all the layers during the time when all layersare simultaneously flowing. The proximity of the innermost interiorlayer and outermost interior layer to the respective inner and outerwalls of the molded article or object is changed by having the flow rateof the combined inner and outer layer be greater or lesser during thetime when all layers are simultaneously flowing.

[0077] Such relative thickness and position of each of the interiorlayers is chosen to enhance the properties of the final molded object.For example, if one of the interior layers is a gas scavenger, thechosen position of the gas scavenger layer may typically be theinnermost interior layer C1 of FIGS. 19 and 19A-D in order to reduce thepermeation rate of gas through the outer layers of the container intothe scavenger, and to increase the rate of gas scavenging from thecontents of the container. Such a position, indeed will extend the shelflife of the container contents if the purpose of the scavenger layer isto absorb gas permeating from the atmosphere exterior to the container.As another example, the position of outermost interior layer C1 of FIG.17 can enhance the performance of a humidity-sensitive gas barrierlayer, such as the before-mentioned EVOH or MXD6 nylon, by moving suchbarrier layer away from the 100% relative humidity of the contents of abeverage that is to fill the container to a position in the wall that iscloser to the lower relative humidity of the atmosphere surrounding thecontainer.

[0078] A typical injection time-line for molding such three-material,four-layer articles wherein the leading edge of the first interior layeris established substantially on the zero-gradient of the velocityprofile, and then a second interior layer is injected and its injectionis finished before the first interior layer injection is finished, asshown in FIGS. 17, 17A-D and 19 and 19A-D, follows: Time, seconds Action0 Close mold 0.1 Start injection of inner and outer layer material atsubstantially 50:50 ratio 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Startinjection of interior layer material substantially on zero- gradient ofvelocity profile 1.1 Start injection of second interior layer materialand reduce combined flow rate of inner and outer material 1.2 1.3 1.41.5 1.6 1.7 1.8 1.9 Finish injection of second interior layer material2.0 Finish injection of first interior layer material substantially onzero-gradient of velocity profile >20 Finish injection of inner andouter layer material

[0079] As previously described, other-shaped objects or articles mayalso be molded by the techniques of the invention, including theflat-shaped articles of earlier mentioned FIGS. 18 and 18A-D and 20 and20A-D.

[0080] Exemplary articles, ports or products formable with theabove-described techniques of the present invention are shown in FIGS.21A through 24C.

[0081]FIG. 21A depicts a plastic molded cylindrical hollow containerhaving an open top and a closed bottom. FIG. 21B shows the cross-sectionof the container through its axial center line (shown dashed), whereinthe interior layer has a leading edge on the centerline of the moldedwall, this centerline corresponding to the zero-gradient of the velocityprofile during the flow of plastic into the mold cavity which formed thepart—for example as in the forming process of FIGS. 7A-C. While theinterior layer leading edge substantially is on the part wallcenterline, the other portions of the interior layer are offset from thecenterline toward the inner wall surface of the article.

[0082] Variants are illustrated in FIGS. 21C and D; with the trailingedge of the interior layer being substantially on the part centerline inFIG. 21C, and with an additional interior layer in FIG. 21D (see FIG.19B, for example) having a leading edge that does not extend as far asthe leading edge of the other interior layer and has a trailing edgethat terminates father from the gate than the other interior layer. Whatis not depicted, but is possible, are molded articles wherein theleading edge of one interior layer extends beyond the leading edge ofthe other interior layer, and wherein the trailing edges of bothinterior layers terminate approximately at the same distance from thegate.

[0083] As another example, FIG. 22D illustrates a blow-molded hollowcontainer formed from the multilayer article of FIG. 22. Cross-sectionsof segments A, B and C of FIGS. 22 and 22D are show on enlarged scalesin FIGS. 22A, 22B and 22C, respectively. FIG. 22 shows a molded preformhaving the leading edge of its interior layer on the wall centerline andother portions of its interior layer offset from the centerline towardthe outer wall surface (as in FIGS. 6A-C). In the wall section in thefinish portion of the article as illustrated wherein the leading edge ofthe interior layer is substantially on the centerline of the wall, andanother portion of the interior layer is offset from the centerlinetoward the outer wall surface. The wall cross-section of a segment ofthe container sidewall is shown in FIG. 22B wherein the interior layeris offset from the centerline toward the outer wall surface; and FIG.22C shows the cross-section of a segment of the container base whereinthe interior layer trailing edge terminates offset from the articlecenterline.

[0084] In the blow-molded container of FIG. 23D, the molded pre-form ofwhich is depicted in FIG. 23, the trailing edge of the interior layer issubstantially on the wall centerline, as distinguished from the pre-formof FIG. 22. FIGS. 23A and 23B are similar to before-discussed FIGS. 22Aand 22B, respectively, but with the variations of FIG. 23. FIG. 23C isthe cross-section C of a segment of the base of the container of FIG.23D wherein the trailing edge of the interior layer terminatessubstantially on the wall centerline.

[0085] Still another modification is presented in the cross-section of afour-layer molded article and FIG. 24 that can be blow-molded into thecontainer of FIG. 24 D (see FIGS. 17-19). The leading and trailing edgesof one interior layer are substantially on the part centerline andextend beyond the leading and trailing edges of the other interior layeras shown, more specifically in FIGS. 24A and 24B, respectively. What isnot depicted, but is possible, are four-layer molded articles forblow-molding wherein the leading edge of the first interior layerextends beyond the leading of the second interior layer and wherein thetrailing edges of both interior layers terminate approximately the samedistance from the gate. An additional undepicted article is one whereinthe trailing edge of the second interior layer extends beyond thetrailing edge of the first interior layer and wherein the leading edgeof the first interior layer extends beyond the leading edge of thesecond interior layer.

[0086] The previously discussed layer distributions of FIGS. 21B, 21C or21D, moreover, can also be molded into articles similar to pre-form ofFIG. 22 for blow-molding into containers similar to FIG. 22D. Similarly,the layer distribution of FIGS. 22, 23 and 24 can also be molded intoarticles similar to FIG. 21. Additionally, any of these depicted layerdistributions can be molded into articles of other shapes, such as flatplates, (see FIGS. 18 and 20), concave discs, lids and closures forcontainers, and other shapes limited only by the imagination of oneskilled in the art.

[0087] Other signs of flow control devices may also be employed, andother further modifications will also occur to those skilled in thisart, such being considered, however, to fall within the spirit and scopeof the invention as defined in the appended claims.

What is claimed is:
 1. A method for co-extruding multiple polymerplastic materials as for injecting through a gate region into a moldcavity to produce a molded article, that comprises, co-extrusivelyflowing streams of polymer plastic materials with at least one interiorstream that is to serve as an interior core of a resulting moldedplastic article within inner and outer streams of plastic material thatserve as covering wall plastic material layers for the core; forcing theflowing streams to flow along concentric annular flow paths within andalong a longitudinally extending tubular extruder nozzle to the cavitygate region; adjusting the flow streams initially to cause the corestream to start to flow at a region of substantially zero gradient inthe transverse flow velocity profile of the extrusion; thereupon varyingthe relative volumetric flow ratio of the inner and outer layer streamsafter the zero-gradient flow of the core layer has started, in order tooffset the core layer flow from the zero gradient and to shift the corelayer closer to one of the inner or outer annular flow boundaries,thereby to produce a molded article wherein the major portion of thecore layer is closer to one of the inner or outer article walls than theother.
 2. The method of claim 1 wherein the relative thickness of theinner or outer layers is correspondingly varied substantially in saidratio.
 3. The method of claim 1 wherein, prior to the termination of theextrusion, the flow ratio of the inner and outer layers is varied toshift the terminal end of the interior core stream back alongsubstantially said zero gradient.
 4. The method of claim 1 wherein theinner and outer stream ratio is varied after a few percent of the corelayer stream flow has initially flowed.
 5. The method of claim 1 whereinthe adjusting of the flow stream initially causes the inner and outerstreams to start to flow with substantially equal volumetric flow rates.6. The method of claim 1 wherein said forcing is effected by disposing alongitudinal pin within and along the extruder to force the combinedstreams into said concentric annular flow paths.
 7. The method of claim1 wherein the relative volumetric flow ratio of the inner and outerstreams is controlled by relatively restricting the respective flowchannels of the streams within the extruder.
 8. The method of claim 7wherein the timing of said relative flow restricting is controlled tocoincide with one or both of (1) a short time after the start of theflow of the core stream, and (2) near the termination thereof.
 9. Themethod of claim 7 wherein the timing of said relative flow restrictingis controlled intermediate the flow of the streams to the mold cavity.10. The method of claim 7 wherein the relative flow restricting iseffected by inserting a flow restrictor into the inner or outer flowstream within the extruder.
 11. The method of claim 7 wherein the inner,outer and core layer flow streams are fed into respective entry channelsin the extruder nozzle from respective material sources, and the flowrestrictor is inserted into one of either a source flow channel, or neara nozzle entry channel.
 12. The method of claim 11 wherein a pluralityof similar nozzles are similarly simultaneously fed from respectivematerial sources, with flow restrictors inserted near correspondinginner or outer layer entry flow channels in each nozzle or in commonfeed channels from said sources.
 13. The method of claim 1 wherein theinner and outer layer streams are fed from the same plastic materialsource and the plastic core material stream from a different source, andthe annular co-extensive streams of the core material stream encased by,the inner and outer layer streams are combined near said gate region andlaterally injected in opposite transverse directions into the moldcavity.
 14. The method of claim 13 wherein the molded article therebyformed is a hollow plastic container in which the interior core layerencased by inner and outer container walls is of material that serves asa barrier layer for such purposes as resisting the flow of gases throughthe container walls and/or scavenging oxygen.
 15. The method of claim 1wherein a three-material plastic article is to be molded comprisinginner and outer layers and two interior or core layer materials andwherein the inner and outer layer material streams are divided withinthe nozzle to form the inner and outer annular covering wall layers, oneof the interior layer streams being directed within the nozzle to forman interior annular layer adjacent said inner layer, and the otherinterior stream being directed within the nozzle to form an interiorannular layer adjacent the outer layer.
 16. A method for co-extrudingmultiple plastic materials as for injecting through a gate region into amold cavity to produce a molded article having an interior core layerencased within inner and outer wall layers, that comprises,co-extrusively flowing inner and outer layer streams of plastic materialencasing an interior core layer to inject the same though the gateregion into the mold cavity; initially starting the flow with asubstantially 50:50 ratio of inner and outer layer stream volumetricflows to cause the interior core stream to flow at a mid-plane region ofsubstantially zero gradient in the transverse flow velocity profile ofthe extrusion; thereupon, for the major portion of the flow, varying therelative volumetric flow ratio of the inner and outer layer streams tooffset the core layer stream from the mid-plane and shift the core layercloser to one of the inner or outer flow boundaries, thereby to producea molded article wherein the major portion of the core layer within thearticle is closer to the inner or outer article wall.
 17. The methodclaimed in claim 16 wherein said flow ratio is varied back tosubstantially 50:50 near the terminal end of the flow into the cavity.18. The method claimed in claim 16 wherein the ratio is varied after afew percent of the core layer stream flow has initially flowed.
 19. Themethod in claim 16 wherein the ratio is further varied during thecontinued flow to the gate region, and into the mold.
 20. The method ofclaim 19 wherein said ratio is varied back to substantially 50:50 nearthe terminal end of the flow to re-establish the interior core streamflow back along substantially said zero gradient.
 21. The method ofclaim 16 wherein the core layer stream material is selected for barrierfunction characteristics such as at least one of gas permeation control,gas-scavenging, and electromagnetic shielding.
 22. Apparatus forco-extruding multiple plastic materials as for injecting through a gateregion into a mold cavity to produce a molded article having an interiorcore layer encased within inner and outer wall layers, the apparatushaving, in combination, a longitudinally extending extruder nozzle forreceiving plastic material from sources thereof and co-extrusivelyflowing the material as inner and outer layer streams of plasticmaterial encasing an interior core layer to inject the same through thegate region into the mold cavity; flow control means for initiallystarting the flow with a substantially 50:50 ratio of inner and outerlayer stream volumetric flow rates to cause the interior core stream toflow at a mid-plane region of substantially zero gradient in thetransverse flow velocity profile of the extrusion; means for thereupon,for the major portion of the flow, adjusting the flow control means tochange the relative volumetric flow ratio of the inner and outer layerstreams to offset the core layer stream from the mid-plane and shift thecore layer closer to one of the inner or outer flow boundaries, therebyto produce a molded article in the cavity wherein the major portion ofthe core layer within the article is closer to one of the inner or outerarticle wall.
 23. The apparatus claimed in claim 22 wherein the flowcontrol means is adjusted to vary the flow ratio back to substantially50:50 near the terminal end of the flow into the cavity.
 24. Theapparatus claimed in claim 22 wherein the flow control means is operatedto change the ratio after a few percent of the core layer stream flowhas initially flowed.
 25. The apparatus claimed in claim 22 wherein theflow control is adjusted to further vary the ratio during the continuedflow to the gate region.
 26. The apparatus of claim 25 wherein the flowcontrol means is adjusted to vary said ratio back to substantially 50:50near the terminal end of the flow to re-establish the interior corestream flow back along substantially said zero gradient.
 27. Theapparatus of claim 22 wherein the core layer stream material is selectedfor barrier function characteristics such as at least one of humiditycontrol, gas permeation, gas scavenging and electromagnetic shielding.28. Apparatus for co-extruding multiple plastic materials as forinjecting through a gate region into a mold cavity to produce a moldedarticle, having, in combination, a longitudinally extending tubularextrusion nozzle provided with entry channels for receiving plasticmaterials from sources thereof and co-extensively flowing the materialsas inner and outer layer streams with one interior stream that is toserve as an interior core of a resulting molded plastic article withininner and outer streams of plastic material that serve as covering wallplastic material layers for the core; a longitudinal throttle means forforcing the streams to flow along concentric annular flow paths withinand along a longitudinally extending tubular-extruder nozzle to thecavity gate region; means for adjusting the flow streams initially tocause the core stream to start to flow at a region of substantially zerogradient in the transverse flow velocity profile of the extrusion; meansoperable thereupon for varying the relative volumetric flow ratio of theinner and outer layer streams after the zero-gradient flow of the corelayer has started in order to offset the core layer flow from the zerogradient and to shift the core layer closer to one of the inner or outerflow boundaries, thereby to produce a molded article wherein the majorportion of the core layer is closer to one of the inner or outer articlewalls than the other.
 29. The apparatus of claim 28 wherein the relativethickness of the inner or outer layers is correspondingly variedsubstantially in said ratio.
 30. The apparatus of claim 28 wherein,prior to the termination of said extrusion, the adjusting means iscontrolled to vary the flow ratio of the inner and outer layers to shiftthe terminal end of the interior core stream back along substantiallysaid zero gradient.
 31. The apparatus of claim 28 wherein the adjustingmeans varies the inner and outer stream ratio after a few percent of thecore layer stream flow has initially started.
 32. The apparatus of claim28 wherein the adjusting means initially causes the inner and outerstreams to start with substantially equal volumetric flow rates.
 33. Theapparatus of claim 28 wherein said adjusting means comprises an axialpin for forcing the combined streams into said concentric annular flowpaths.
 34. The apparatus of claim 28 wherein the relative volumetricflow ratio of the inner and outer streams is controlled by restrictorsdisposed in the respective flow channels of the streams within theextruder.
 35. The apparatus of claim 34 wherein means is provided forcontrolling the timing of the relative restricting by the restrictors tocoincide with one or both of shortly after the start of the flow of thecore stream, and near the termination of the core stream flow.
 36. Theapparatus of claim 35 wherein means is provided for controlling thetiming of the relative flow restricting intermediate the flow of thestreams to the mold cavity.
 37. The apparatus of claim 35 wherein therelative flow restricting is effected by means for inserting a flowrestrictor into one of the inner or outer flow streams.
 38. Theapparatus of claim 28 wherein the inner, outer and core layer flowstreams are fed into respective entry channels in the nozzle fromrespective material sources, and the flow restrictor is inserted intoone of (1) a source flow channel or (2) near a nozzle entry channel. 39.The apparatus of claim 28 wherein a plurality of similar nozzles isprovided, the nozzles of which are similarly simultaneously fed fromrespective material sources, with flow restrictor means inserted incorresponding inner or outer layer entry flow channels in each nozzle orin common feed channels from said sources.
 40. The apparatus of claim 28wherein the inner and outer layer streams are fed from the same plasticmaterial source and the plastic core material stream from a differentsource, and the annular co-extensive streams of the core material streamencased by the inner and outer layer streams are combined near said gateregion and laterally injected in opposite transverse directions into themold cavity.
 41. The apparatus of claim 40 wherein the molded articlethereby formed is a hollow plastic container in which the interior corelayer is of material that serves as a barrier layer for such purposes asresisting the flow of humidity and or gases through the container wallsand/or scavenging oxygen through chemical combination therewith.
 42. Theapparatus of claim 28 wherein a 3-material plastic article is to bemolded comprising inner and outer layers and two interior or core layermaterials, and wherein the inner and outer layer material streams aredivided within the nozzle to form the inner and outer annular coveringwall layers, one of the interior layer streams is directed within thenozzle to form an interior annular layer adjacent said inner layer, andthe other interior stream is directed within the nozzle to form aninterior annular layer adjacent the outer layer.
 43. The method of claim1 wherein a plurality of similar extruder nozzles is provided similarlysimultaneously fed from respective material sources, and with flowrestriction inserted in corresponding inner and outer layer entry flowchannels into each nozzle or in common feed channels from said sources.44. The method of claim 1 wherein two interior streams are flowed withinsaid inner and outer streams, with the flow of one of the interiorstream started before the flow of the other interior stream and with itsleading edge starting on said zero-gradient, and the subsequentinitiation of the flow of said other interior stream offsetting thelater-flowing portions of said one interior stream flow from said zerogradient, and with the completing of the injecting of the other interiorstream before the completion of the injecting of said one interiorstream through said gate region and into said mold cavity, and finishingthe injecting of said interior stream on said zero gradient.
 45. Themethod of claim 44 wherein the materials of the inner, outer andinterior streams constitute three molding materials forming a four-layermolded article.
 46. The method of claim 45 wherein the relativethickness and position of each of the interior streams is chosen toenhance the properties of the molded article.
 47. The method of claim 46wherein the innermost of the interior streams is of gas scavengingmaterial in order to reduce the permeation rate of gas through saidouter wall of the molded article, and to increase the rate of gasscavenging from the contents of the article if the scavenger material isintended to absorb gas permeating from the exterior of the article. 48.The method of claim 46 wherein the outermost of the interior streams isof humidity sensitive gas barrier material in order to position suchbarrier at a position within the molded article that is closer to theexterior atmosphere surrounding the article.
 49. The method of claim 44wherein the article is one of a cylindrical-shaped hollow container,such as a bottle, and a flat-shaped article.
 50. The apparatus of claim22 wherein said inner core layer comprises a pair of interior corestreams, with said adjusting means enabling one of the interior streamsto start flow before the other of the pair of interior streams and withits leading edge starting on said zero gradient, and enabling thesubsequent initiation of the flow of said other interior streamoffsetting the later-flowing portions of said one interior streamthrough said gate region and into said mold cavity, with the finishingof the injecting of said one interior stream lying on said zerogradient.
 51. The apparatus of claim 50 wherein the materials of theinner, outer and interior streams constitute three molding materialsforming a four layer molded article.
 52. The apparatus of claim 51wherein the relative thickness and position of each of the interiorstreams is chosen to enhance the properties of the molded article. 53.The apparatus of claim 52 wherein the innermost of the interior streamsis of gas scavenging material in order to reduce the permeation rate ofgas through said outer wall of the molded article, and to increase therate of gas scavenging from the contents of the article if the scavengermaterial is intended to absorb gas permeating from the exterior of thearticle.
 54. The apparatus of claim 52 wherein the outermost of theinterior streams is of humidity sensitive gas barrier material in orderto position such barrier at a position within the molded article that iscloser to the exterior atmosphere surrounding the article.
 55. Theapparatus of claim 50 wherein the article is one of a cylindrical-shapedhollow container, such as a bottle, and a flat-shaped article.
 56. Amolded plastic material article having an interior plastic core layerencased within inner and outer plastic wall layers wherein the majorportion of the core layer within the article is closer to one of theinner or outer article walls.
 57. The molded article of claim 56 whereinthe article is hollow and bounded by the core-encased inner and outerwalls.
 58. The molded article of claim 57 wherein the initial portionthe core layer lies substantially on the centerline of the core-encasedinner and outer article walls.
 59. The molded article of claim 58wherein said initial portion constitutes a few percent of the length ofthe core layer.
 60. The molded article of claim 59 wherein the corelayer near its terminal end again lies-substantially on said centerline.61. The molded article of claim 59 wherein the core layer material isselected for barrier function characteristics such as at least one ofhumidity control, gas permeation, gas scavenging and electromagneticshielding.
 62. The molded article of claim 59 wherein the inner andouter walls and the core are of three molding materials forming afour-layer molded article.
 63. A pre-form for a hollow molded plasticmaterial article having an interior plastic core layer encased withininner and outer plastic wall layers wherein the major portion of thecore layer within the pre-form is closer to one of the inner and outerarticle walls.
 64. The pre-form of claim 63 wherein the initial portionof the core layer lies substantially on the centerline of thecore-encased inner and outer article walls.
 65. The pre-form of claim 64wherein said initial portion constitutes a few percent of the length ofthe core layer.
 66. The pre-form of claim 65 wherein the core layer nearits terminal end again lies substantially on said centerline.
 67. Thepre-form of claim 65 wherein the core layer material is selected forbarrier function characteristics such as at least one of humiditycontrol, gas permeation, gas scavenging and electromagnetic shielding.